This is a known problem by Apple, read [http://9to5mac.com/2012/04/04/apple-investigating-new-ipad-wifi-issues-tells-applecare-to-replace-affected-units/|this] article for more info.
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Theres probably something wrong with the WiFI chip, you should return your iPad+AC charger+usb cable to your reseller and then you'll get a new one.